The present invention relates to a thermal image detecting system using a pyroelectric type thermal detection element provided, for example, for detection of room temperature distribution in a house or for detection of the behavior of a human body.
The conventional non-contact temperature measuring system includes a quantum type infrared ray sensor or a thermal infrared ray sensor. The quantum type infrared ray sensor is characterized in that it has a high sensitivity and hence a rapid response speed. However, the sensor must be cooled (to about -200.degree. C.). Therefore, this sensor is unsuitable for consumer use. On the other hand, the thermal infrared ray sensor has relatively low sensitivity and a slow response speed, but does not have to be cooled. Therefore, this sensor has been sold in the consumer market. In particular, a pyroelectric type infrared ray sensor using the pyroelectric effect is widely used.
The pyroelectric infrared ray sensor has a differential change output characteristic so that an output is generated only when the incident temperature changes. In the pyroelectric infrared ray sensor hitherto employed, a Fresnel lens using a polyethylene resin and having an angle of view with a light distribution characteristic is provided on the entire surface of the sensor. When a human body moves, the radiation temperature of the human body is inputted to the sensor as a time changing input in accordance with the light distribution characteristic. An output of the pyroelectric infrared ray sensor is provided in synchronism with the time changing input, thereby making it possible to detect the human body. On the other hand, when a human body is in a stationary state, the detection of the human body is not possible since a time changing input to the sensor is not provided.
Also, other known types of sensors are pyroelectric infrared sensors which are made of ceramics and point temperature sensors which use a chopper. However, since these sensors have low sensitivity and a very slow response speed, it is not possible to detect large amounts of temperature data within a period of one or two seconds. Further, a system has been considered in which pyroelectric infrared sensors are two-dimensionally arranged to achieve a temperature distribution measuring means.